Albino Zebras and Leopards

Changing their Spots

Responding to a query, " Could someone please tell
me if it's true there have been reported albino zebra sharks (Stegostoma
fasciata)? And, if so, how do they look like? Are the stripes and then the
spots lighter or just gone? What about the eyes, are they red?", I wrote:

In 1973, Nakaya reported a partial albino of Stegostoma varium (= fasciatum)
taken from the Indian Ocean during January of 1964 (Jap.J.Ichthyol.,
20[2]: 120-122). The specimen was a mature female, 185 centimetres long, having
a uniformly white body with a very slight red tint (blood/blood vessels near the
surface of the body and visible through the translucent skin?); it lacked all
traces of the black spots or blotches usually present in adults of this species,
but the fin margins were greyish. The irises of this specimen were
blackish-brown, much as in normally pigmented individuals of this species,
leading Nakaya to suggest it was a partial albino. Nakaya notes it is
interesting this specimen had grown as large as it had, suggesting that a very
pale shark would be quite conspicuous against a darker bottom and perhaps be
more vulnerable to predation.

In true albinism, epistatic genes block expression of the gene coding for
tyrosinase, the first of a series of enzymes needed to produce pigmentation.
Without tyrosinase, no pigment whatever can form. At least six other epistatic
blocks can occur along the conversion route. If they occur at later steps,
slight amounts of pigment still form and imparts some color to the individual
(as in Nakaya's partial albino Stegostoma).

There may be a link between tyrosine (which is acted upon by tyrosinase) and
aggression, which  in turn  may have implications for breeding behavior and,
ultimately, for reproductive success in vertebrates. An alternative pleitropic
pathway leading to the production of certain monoamines results in
neurotransmitters which control motivational systems in the vertebrate brain.
Therefore, a gene acting on a pathway leading to tyrosine might influence
simultaneously *both* body color and aggressive behavior. A polymorphism is
known in birds in which these traits vary concordantly. For example, in a
European bird known as the Ruff
(Philomachus pugnax), the melanistic form is more aggressive than and
dominant over the lighter form. The possibility exists that the social organization
on the lek of the Ruff has been influenced by a mutation in the
tyrosine pathway.

Thus albino or other pale color morphs of sharks  particularly in males  may reduce assertiveness during courtship and reduce the likelihood of
successful mating in such individuals.

Also, whale sharks do keep the exact same marks they're
born with all their lives. Right?

Probably, but this has not been verified experimentally. Tagging of Whale
Sharks is a relatively recent activity and no one  to my knowledge, at least 
has tagged a neonate of this species and observed its pigmentation pattern for
changes throughout its lifetime (however long that might be  25 years?).

Leopard Shark (Triakis semifasciata)

If you remember any piece of curious information about
Leopard Sharks (Triakis semifasciata)

Off the top of my head:

a true albino of Triakis semifasciata has been reported, lacking
all traces of the dark spots and saddles typical of this species and
complete with pink irises

off California, adults of this species regularly feed on echiuran
Innkeeper Worms (Urechis caupo), actually sucking them from their U-shaped
burrows in the mud and swallowing them whole

Leopard Sharks sometimes mutilate their prey, consuming only a part of
them  such as seizing the extended siphons of buried clams and ripping
them off with violent lateral head-shaking; it is not uncommon to find
dozens of fleshy bivalve siphons (no bivalves, just the siphons) in stomachs
of these sharks

although generally regarded as harmless, there is a report of a leopard
shark charging a skin diver with a nosebleed

Another voice added: " are there parts of the
world where they refer to zebra sharks as leopard sharks, or vice versa?

Both names are correct, although one has advantages over the other and is
thus preferentially used.

Juvenile Stegostoma varium (= fasciatum)  less than 50 cm long  sport a
striking pigmentation pattern, consisting of chocolate brown back and flanks
broken into irregular saddles by thin yellowish vertical bars and spots
extending upward from the pale yellow belly and the tail is similarly marked. At
this life history stage, the animal is well described by the common name 'zebra
shark'. Between lengths of about 50 and 90 cm, however, zebra sharks' saddles
break up into small brown spots and faint brownish splodges on a yellowish
background, the markings becoming less linear and the spots more uniformly
distributed with growth. Although there is considerable variation in the precise
pigmentation pattern among individuals of this species, by the time zebra
sharks are adult, their back and flanks are pale yellow to yellowish-brown
sprinkled with small dark brown to black spots. At this life history stage, the
name 'zebra' seems downright inappropriate and the species is often referred to
as by the more descriptive name, 'leopard shark'.

Although vernacular names are not governed by the sort of stringent rules
which constrain scientific binomia, it is a general tradition that the common
name of an organism describes the adult rather than the juvenile phase (hence,
to cite two piscine examples, the names Bluehead Wrasse and Blue Tang are used
for Thalassoma bifasciatum and Acanthurus coeruleus, respectively,
both of which are bright yellow as juveniles). But there is a boldly saddled and
spotted but unrelated smoothhound of the family Triakidae (Triakis
semifasciata) which is also widely known as the leopard shark; in addition,
the name 'leopard shark' has in the past been fairly widely used for the Tiger
Shark (Galeocerdo cuvier) of the family Carcharhinidae.

So, to avoid confusion, the unique name 'Zebra Shark' became preferentially
used for Stegostoma varium (= fasciatum).

The Zebra Shark  What's in a Name

The question: Is the scientific name for the Zebra Shark Stegostoma
fasciatum or S. varium, or, are there more than one species in the
genus? I responded:

No, the genus Stegostoma seems to be monotypical (represented by a
single species).

One of the fundamental rules about the establishment of scientific names is
that the earliest proposed binomen (two-part name, composed of a paired genus
and species) that is accompanied by a formal description (detailing precisely
how the purported new species differs from all similar species  preferably buttressed
by the designation of a curated 'holotype', or representative
specimen, which thereafter serves as the ultimate standard for comparison). But,
as with many other rules, there are exceptions. For historical reasons (about
which more later), 1758 is the arbitrary cut-off date for scientific names, and
no name proposed before that date will be considered. Sometimes, however  due
to logistical hurdles, such as publication in an obscure journal that has been
largely overlooked by taxonomists  the earliest valid name is not discovered
until long after a younger name has attained widespread use. In such cases, the
International Commission on Zoological Nomenclature (ICZN)  of which I have
previously written  will exercise its plenary powers to formally suppress an
older, largely unused but otherwise valid name and declare the younger but
widely-used name as the binomen to be preferentially used by taxonomists.

For example, most of us know the Oceanic Whitetip Shark as Carcharhinus
longimanus. This species was named Squalus longimanus by Poey in
1861, based on a 164-cm male specimen from Cuba. ( This species has been placed
in various genera over the years  most notably Pterolamiops, proposed
by Springer in 1950, but was first placed in its current genus by Garman in
1881, under the name Carcharhinus obtusus, which was formally reinstated
as the preferred genus by Garrick in 1982, who advocated the now-familiar name, Carcharhinus
longimanus.) But, it turns out, that the same species had already been
described as Squalus maou by Lesson in 1830, based on two specimens about
122 cm in standard length (straight line distance from the tip of the snout to
the upper precaudal pit) from the Paumoto Archipelago (now better known as the
Tuamotu Archipelago, in French Polynesia). No holotype was designated, but
Lesson did provide an unmistakable illustration of his purported new species 
in the widely-available Reader's Digest book, Sharks: Silent Hunters of the
Deep (on the lower left of page 68), you can check out a full-color reprint
of the original illustration that accompanied Lesson's description. The drawing,
done by an artist (whose name I have not yet been able to discover) on board
Duperrey's 18221825 Pacific voyage on the Royal French Corvette Coquille,
is rather stylized (as was common in natural history illustrations of the time)
but clearly represents a small male Oceanic Whitetip. Yet Lesson's description,
published in French as part of the zoological account of the voyage of the Coquille,
lay buried and largely unnoticed among the book's 471 pages. From his 1982
revision of the genus Carcharhinus, Garrick was clearly aware of Lesson's
description and accompanying illustration, but  in the interests of taxonomic
stability  opted to retain the more-familiar and widely-in-use name longimanus
in favor of the older, valid-but-obscure name, maou. This has been
followed by Compagno in his 1984 FAO catalogue, Sharks of the World, and
subsequently by most ichthyologists and shark enthusiasts (myself included 
for practical as well as poetic reasons: longimanus means "long
hands", which nicely describes the paddle-like pectoral fins of this
species; maou is simply derived from a local word for "shark").
But until the ICZN makes a formal ruling on this matter, technically, Carcharhinus
maou (Lesson) 1830 is the oldest valid name for the Oceanic Whitetip and the
name which has priority.

And so, having established the relevant theoretical framework, on to the Stegostoma
issue which prompted your inquiry.

At first glace, it doesn't make a lot of
sense to call a spotted shark "zebra". But the Zebra Shark
(Stegostoma varium) starts out life sporting
strongly contrasting bars of black and yellowish-white. As the shark
ages, these bars break up into linear patterns of spots. These
spots, in turn, break up into the leopard-like pattern seen here.

As far as taxonomic scholars can tell, the Zebra Shark was first described by
Seba in 1758 as Squalus varius, probably based on specimens from
Indonesia. Seba's description (in Latin) is comprehensive and accurate, and 
although no holotype was designated  is supported by a good illustration of a
juvenile (with a caption in French). This species was placed in the genus Stegostoma
by Mόller and Henle in 1837, under the name fasciatus, following yet
another pair of taxonomists, Bloch and Schneider, based on their standard text
of 1801. Compagno (1984) followed Mόller & Henle in adopting Stegostoma
as the genus for the Zebra Shark, but rejected the species name varius,
on the grounds that Seba's nomenclature was not consistently binomial,
preferring to use the next-oldest species name fasciatum, based on Herman
1783. The classificatory scheme used by all modern biologists is based on one
originally proposed by botanist Linne (Linnaeus) in the 10th edition of his Systema
Naturae, published in 1758. Latin names had been used long before then, but
they were highly variable in structure (ranging from a single word to long,
complex descriptive sentences or paragraphs); in 1758, Linne changed all that
when he formally proposed the binomial system of nomenclature, a standardization
which was quickly adopted by the scientific community. In honor of this
achievement, 1758 remains the arbitrary cut-off date for the earliest acceptable
binomial. As acclaimed ichthyologist Randall points out in his excellent 1986
book, Sharks of Arabia (p 70), even if many Seba names are non-binomial,
his Squalus varius most definitely is. As a result, Randall adopts the
name Stegostoma varium for the Zebra Shark. (In case you're wondering, varium
is the preferred Latin form of for the species name in this case, as ICZN rules
dictate that species epithets used as adjectives in the nominitive singular must
agree in gender with the generic name.* ) In any event, Randall's reasoning
makes perfectly good sense to me, and  since Seba's description and
illustration are unambiguous, his name does not violate the 1758 cut-off date,
and the name varius ("variable") nicely reflects the dramatic
pigmentation and proportional changes this species undergoes as it matures
[while fasciatum ("banded") reflects only the juvenile phase]
 for the Zebra Shark, I prefer to use the name Stegostoma varium .

As Confucius reputedly once put it, "The beginning of wisdom is to call
things by their right name". But it is well to bear in mind that using the
'correct' name is merely a beginning. It's what you do with this knowledge
that counts.